I have an application which sometimes fails saying that it can't create a directory, because it already exists. The directory is created by fs::create_directories("run"); and the application is multi-threaded. It seems there's a race condition: if (ph.empty() || exists(ph)) return; // First create branch, by calling ourself recursively create_directories(ph.branch_path()); // Now that parent's path exists, create the directory create_directory(ph); After one thread checks that 'ph' does not exist, another one creates the same directory, so call to 'create_directory' fails. What can be done? Basically, adding a mutex for MT build and adding a warning to docs are the variants. Opinions? - Volodya